Valves are commonly used in process control systems to control the flow of process fluids. Linear valves (e.g., a gate valve, a globe valve, a diaphragm valve, a pinch valve, etc.) typically have a closure member (e.g., a valve plug) disposed in a fluid path. A valve stem operatively couples the closure member to an actuator that moves the closure member between an open position and a closed position to allow or restrict the flow of fluid between an inlet and an outlet of the valve. Additionally, to achieve certain fluid flow characteristics, valves often employ a cage that interposes in the fluid flow path between the inlet and the outlet of the valve. A cage can reduce flow capacity, attenuate noise, and/or reduce or eliminate cavitation. Additionally, a cage surrounds the closure member to provide stability, balance, and alignment to the closure member.
To effect a seal of a closure member, the closure member typically includes a channel or groove that receives a seal that engages an inner surface of the cage. Typically, industrial process conditions such as pressure and temperature (e.g., super-heated steam applications) of the process fluids dictate the type of valve and valve components that may be used such as, for example, the types of seals that may be used to effect a seal of a closure member. For high temperature applications, flexible valve seals (e.g., an elastomeric seal) cannot be used due their inability to withstand high temperatures.
In high-temperature applications (e.g., greater than 450° F.), because of its resistance to high temperature, a carbon-fiber sealing ring may be used. However, because of its brittle characteristic and lack of elasticity, a carbon-fiber seal cannot be installed intact and must be broken into pieces prior to being installed in a groove of the closure member. The fractured mating ends of the sealing ring pieces may ultimately cause undesired leakage. Additionally, the pressure differential of the fluid between the inlet and the outlet of the valve is used to pressure assist or load the seal against the sealing surface (i.e., the groove of the closure member) to effect a seal of the closure member. However, during low pressure conditions, the fluid pressure may be insufficient to pressure assist the seal against the sealing surface, thereby causing undesired leakage through the valve.